QQ群友提出的问题，

当问点编组设置用户自定义属性分类并修改自定义属性值后，

想删除自定义属性时提示属性正在使用，

无法删除.....

为实现删除功能，

使用COM API，

顺利实现删除。

测试代码如下：

civil 3d版本为2022，

"AeccXUiLand.AeccApplication.13.4";中的13.4需要根据使用的civil 3d版本就行修改，
注释掉的代码不能实现自定义属性的删除。

public void C_TestUDP()
{
    Document doc = Application.DocumentManager.MdiActiveDocument;
    CivilDocument civilDoc = CivilApplication.ActiveDocument;
    PointGroup pg;
    using (Transaction tr = doc.TransactionManager.StartTransaction())
    {
        PointGroupCollection pgcs = civilDoc.PointGroups;
        foreach (ObjectId id in pgcs)
        {
            pg = id.GetObject(OpenMode.ForWrite) as PointGroup;
            pg.UseNoneClassification();
        }

        tr.Commit();
    }
    //using (Transaction tr = doc.TransactionManager.StartTransaction())
    //{
    //    UDPClassification udpc;
    //    if (civilDoc.PointUDPClassifications.Contains("桩参数"))
    //    {
    //        udpc = civilDoc.PointUDPClassifications["桩参数"];
    //        for (int i = udpc.UDPs.Count - 1; i >= 0; i--)
    //        {
    //            udpc.RemoveUDP(udpc.UDPs[i]);
    //        }
    //    }
    //    tr.Commit();
    //}
    string m_sAcadProdID = "AutoCAD.Application";
    string m_sAeccAppProgId = "AeccXUiLand.AeccApplication.13.4";
    var m_oAcadApp = (IAcadApplication)System.Runtime.InteropServices.Marshal.GetActiveObject(m_sAcadProdID);
    var m_oAeccApp = (IAeccApplication)m_oAcadApp.GetInterfaceObject(m_sAeccAppProgId);
    var m_oAeccDoc = (IAeccDocument)m_oAeccApp.ActiveDocument;
    var m_oAeccDb = (AeccDatabase)m_oAeccApp.ActiveDocument.Database;
    var m_oAeccudpc = m_oAeccDb.PointUserDefinedPropertyClassifications.Item("桩参数");
    try
    {
        for (int i = m_oAeccudpc.UserDefinedProperties.Count - 1; i >= 0; i--)
        {
            m_oAeccudpc.UserDefinedProperties.Remove(i);
        }
    }
    catch (System.Exception ex)
    {
    }
}